Control system



Jul 27, 1943. A EDWARDS ET AL 2,325,381

CONTROL SYSTEM Filed March 25, 1941 2 Sheets-Sheet 1 Inventors I Martin A. Edwards,

David R. Shoulbs,

Their Attorney July 27, 1943.

M. A. EDWARDS ET AL 2,325,381

CONTROL SYSTEM Filed March 25, 1941 2 Sheets-Sheet 2 Fig.2.

as 5a 52 F T .5 L I W Inventor's Martin A. Edwards,

' David R. Shoults,

. by y fj Their Attorney.

Patented July 27, 1943 2,325,381 con'raor. SYSTEM Martin A. Edwards, Scotia, and David R.

Schenectady, N. Y., assign Shoult s, ors to General Electric Company, a corporation of New York v Application March 25, 1941, Serial No. 385,098 I 13 Claims.

This invention relates to control systems, moreparticularly to systems for controlling the operation of apparatus having an element operating on a length of material and 'a second element operating on the material after it is delivered from the first element, and it has for an object the provision of a simple, reliable and improved system of this character.

More specifically, the invention relates to a control system of this character in which it is desirable to maintain a predetermined tension in the material between the elements which operate successively on the material, and a further object of the invention is the provision of improved means for maintaining constant tension in the material between the elements operating thereon.

Another object of the invention is the provision of improved means for maintaining a stalled tension in the material, i. e., for maintaining a predetermined tension in the material when the apparatus is stopped.

A still further object of the invention is the provision of means for forcing the energization of the driving means for the second or subsequently operating element during acceleration 'and for fozcing its deenergization during deceleration in order to counteract variations in the tension of the material which would otherwise be present as a result of the inertia of the parts of the tension-controlling means.

In illustrating the invention in one form thereof, it is shown as embodied in a control system for the winder rolls of a sectionalized papermaking machine.

For a better and more complete understand ing of the invention, reference should now be had to the following specification and to the accompanying drawings in which Fig. l is a simple diagrammatical illustration of an embodiment of the invention, and Fig. 2 is a simple diagramtension of the web 10. The force exerted by the web against the dancer roll l2, i. e., the tension in the web is counterbalanced by weights ll is included in circuit with the field winding 32a and l'h which are connected to the dancer roll l2 by means of cables l8 and I8- respectively. The cable passes over a rotatably mounted pulley IS.

The calender stack II is driven by any suitable driving means, such as the electric motor 20, to the shaft of which the calender stack is connected through suitable reduction gearing 2|. Although the motor 20 may be of any suitable type it is illustrated as a direct current motor and is supplied from a suitable *Source of voltage such as represented by the adjustable voltage generator 22 to the armature of which it is connected by means of conductor 23. a. The driving rolls 24 of the winder mechanism are separately driven by means of suitable electric motors 25 and 26, respectively, to which they are connected through reduction gearing 2'! and 28, respectively. The motors 25 and 26 are supplied from a suitable source such as the adjustable voltage generator 29. The motor 20 is provided with a field winding 20a and similarly the motors 25 and 26 are provided with field windings 25,. and 283,, respectively. These field windings 20a, 25a and 25a are connected to a source of excitation represented by the conductors 30 and 3| which are supplied from a self-excited generator 32. The adjustable voltage generator 22 is provided with field winding 22s, and this field winding is also supplied from the excitation buses 30 and 3|. justable voltage generators 22 and 29 and exciter 32 are mounted on a common shaft and are driven at a speed which is preferably substantially constant by suitable means illustrated as an induction motor 33 which is supplied from a suitable source of polyphase voltage represented by the three supply lines 34. The exciter 32 is provided witha self-excited shunt field winding 32a, and an adjustable resistor 32s to provide for adjusting the excitation of the exciter to a desired value. A resistor 35, provided with a movable contact 35. to provide for adjustment thereof, is included in the circuit with the field winding 22-. of generator 22 for adjusting the voltage of the generator and thereby adjusting the speed of the calender stack mm tor 20 to a desired value. 'The speed range of the motor 20 may be extended beyond the range that is obtainable by adjustment of the armature voltage by means of a resistor 36 which is included in the circuit of the field winding 20- As indicated in the drawings, ad-

contact arm 36a for adjusting the resistance to the desired value.

It will be noted that an equalizing resistor 31 is included in the connections between the field windings 259. and 26a and the side 38 of the excitation source and is provided with a movable contact 31a to provide for relative adjustment of the amounts of resistance in circuit with each of the field windings 25a and 268.. This equalizing resistor 31 is adjusted until the motors 25 and 26 divide the winding load equally. It is necessary that the winder motors 25 and 26 operate in va predetermined speed relationship with the motor 28 in order that the web in shall not be broken or a loop formed therein. For

the purpose of maintaining this desired speed relation, suitable means are provided for controlling the supply of current from the adjustarmature reaction excited dynamo-electric machine 48 which is mounted on the shaft with the generators 22, 29 and 32 and driven by the motor 33. The tachometer generators 38 and 39 are provided with field windings 38a and 39a respectively which are connected to the excitation buses and 3|. The armature reaction excited dynamo-electric machine 48 is provided with a pair of short circuited armature brushes 48s, a pair of load brushes 48b, and a control field winding 48s. The armatures of the tachometer generators 38 and 39 are connected difierentially to the control field winding 48a of the armature reaction excited dynamo-electric machine 48. The circuit of the control field winding 40c may be traced from the upper terminal of the field winding 400 through conductor 4|, the armature of tachometer generator 38 and conductor 42, to the movable contact arm 43a of a variable resistor 43, thence in parallel through both branches of resistor 43, conductors 44 and 45 in parallel to the opposite terminals of a variable resistor 46 and thence through the movable contact arm 46a, conductor 41, the armature of tachometer generator 39 and conductor 48 to the lower terminal of the control field winding 48c. It will be noted that the varistat 31 so that the field current for the winder motors fiows through resistor 46. The field current flowing through resistor 46 produces a voltage drop and since the resistor 43 is connected in parallel with resistor 46, the same voltage drop exists across resistor 43. The circuit for the controlfield winding 40 of the armature reaction excited dynamo-electric machine 48 was traced through resistors 43 and 46 in parallel and consequently a voltage will be impressed upon the field winding 48. In other words, the resistors 43 and 46 are connected as potentiometers' and the opposite terminals of the field winding 486 are connected through the armatures of the tachometer generators 38 and 39 to the movable contact arms 43a and 46a of resistors 43 and 46., The magnitude of the voltage which is impressed upon the .field winding 48 therefore depends upon the relative positions of the contact arms 43. and 46s on the resist rs 49 and 46.

The field winding 29a of the generator 29 which supplies the winder motors 25 and 26 is connected to the load brushes 48b of the dynamoelectric machine 40.

A variable resistor 49 is included in the field circuit of the tachometer generator 38 between the lower terminal of the field winding 38a and the uppe side 30 of the excitation source. It is provided with a movable contact arm 49s and, as shown in the drawings, the movable contact arms 43a and 49a of rheostats 43 and 49 are secured to a shaft 58 which in turn is secured to the pulley I9 so as to rotate therewith.

With the foregoing understanding of the elements and their organization in the system, the operation of the completed system will be readily understood from the following detailed description; Assuming that the induction motor 33 is in the web I8 is initially set at the desired value tor 20 and similarly the tachometer generator 39 generates a voltage proportional to the speed of the winder driving motors 25 and 26. The diiference of these voltages is applied to the control field winding 00 of the armature reaction excited dynamo-electric machine 48. The initial adjustments are such that when the calender stack I l and the winder mechanism are in proper step with each other the difierence between the voltages of tachometer generators 38 and 39 will energize the control field winding 48s of machine 40 to the extent required to cause the supply generator 29 to supply the amount of current to winder motors 25 and 26 to cause them to operate in the desired predetermined speed relationship with motor 28. In other words, a balanced condition obtains.

If the tension in the web 18 decreases from the desired value, the force of the web against the dancer roll i2 will no longer balance the pull of the weights I1 and He. Consequently, the weights l1 and "a will descend and will rotate the contact arm 49s in a clockwise direction to increase the amount of the resistance 49 in the circuit of the field winding 38a of tachometer generator 38. This increase in resistance decreases the voltage of tachometer generator 38. As a result, the difierential voltage of the tachometer generators 38 and 39 is increased and this increases the excitation of the field winding 46c of dynamo-electric machine 48. This in turn increases the voltage of the machine 48 and the excitation of the field winding 299; which is supplied from the machine 40. The increased excitation of adjustable voltage generator 29 causes an increased voltage to be supplied to the winder motors 25 and 26 and this results in increasing the speed of these motors. The increased speed of the winder motors 25 and 26 increases the winding speed of the web ID on the roll and thereby increases the tension in the stack. This action continues until the tension in the web is again exactly balanced by the pull of the weights I1 and 1a at which time the system will again attain a balanced condition.

If the tension in the web l increases above the desired predetermined value, the force of the web against the dancer roll I 2 will overpower the pull of the weights I l and '18 and move the dancer roll l2 in a clockwise direction thereby to rotate the contact arm 49a in acounterclockwise direction to decrease the amount of resistance in the field circuit of the tachometer generator 38. As a result, the voltage of tachometer generator .38 is increased and the difierenti'al voltage of tachometer generators 38 and 39 is decreased thereby decreasing the energization of the control field winding 40 of dynamoelectric machine 40.

This results in decreasing the energization of the field winding 299. which in turn results in decreasing the voltage supplied to the winder motors 25 and 26. As the speed of the motors 25 and 26 decreases, the speed at which the web I0 is wound on the winding roll is decreased so that the tension in theweb between therolls and the calender stack II is decreased. The tension in the web will continue to decrease until it reaches the desired predetermined value at which time the balanced condition of the system is reestablished.

The machine may be stopped by moving the contact arm 36a of rheostat 36 in a counterclockwise direction to strengthen the field of the motor and by moving the contact arm 35. of the rheostat 35 in a clockwise direction to weaken the field of the,supp ly generator 22 there-- fore no difierential voltage is supplied from thetachometer generators to the field winding 40 of the dynamoelectric machine 40. The tension in the web does not disappear, however, because a voltage is supplied to the control field winding 40c of the dynamoelectric machine 40 as a result of its connection to the rheostai's 43 and 45. Although the apparatus is at rest the field windings 25a and 2a. of windermotors 25 and 26 are still energized and the field current for these windings flows through the resistor 46 thereby producing a voltage drop across resistor 48 and resistor 43 which is connected in parallel therewith. Consequently, a voltage is applied to the field wind-- ing 400 since its opposite terminals are connected I through the armatures of the tachometer generators 38 and 39 to the contact arms 43a and 451i .of rheostats 43 and 45. The magnitude of this voltage which is impressed on the field winding 40 will depend upon the relative positions of the contact arms 43a and 46s on the resistors 43 and 45 respectively.

23 to cause it to supply that amount of current to the motors 25 and 25 that is necessary to increase the tension in the web ill to the predetermined value at which the pull of the weights l1 and I1. is balanced and the balanced condition of the system reestablished.

The modified system of Fig. 2 difiers from the system of Hg. 1 in that the winder motors 5| and 52 are supplied from the generator 53 which supplies the calender roll stack driving motor 54. Since the winder roll motors 5| and 52 are sup plied from the generator which supplies the calender stack motor 54, the armature reaction excited dynamoelectric machine 55 cannot be connected to the field winding 53.. of generator 53 because the winder roll motors 5| and 52 must be controlled independently oi the motor 54 in order to maintain the desired tension in the web 55 between the calender stack 51 and the winding roll 58. Consequently, a booster generator 53 is included in series relationship in the connections between the supply generator 53 and the armatures oi the winder motors 5| and 52 and the field winding 59. of this booster generator is supplied irom the load brushes of the tion excited dynamoelectric machine 55.

The operation oi. the modified system of Fig. 2 to maintain tension is substantially the same as that described in the foregoing for Fig. 1 with the exception that the output or the armature reaction excited dynamoelectr-ic machine 55 is applied to the field winding 59 of the booster generator 59 to bring about the necessary increase or decrease in the current supplied to the winder motors 5| and 52 to maintain the desired tension in the web 55.

The modified system of Fig. 2 has-an added improvement over the system of Fig. 1. During acceleration and deceleration of the apparatus, changes in the tension of the web 56 from the desired value tend to result from the sluggishness or inertia of the parts of the tension control mechanism in responding to changes in the tension of the web to cause the winder motors to change speed in step with the back roll driving motor. These changes in tension are, of course,

undesirable, and in the modified system of Fig. 2,

means are provided for eliminating these undesirable changes in tension which result during acceleration and declaration. These means are illustrated as comprising an auxiliary control field winding 55b wound on the same axis with the main control field winding 55a of armature reaction excited dynamo'electric machine 55 and a transformer 60. This transformer 50 has a secondary winding 60a connected to the auxiliary field winding 55b and two primary windings 60b and 50. The primary winding 50s is connected across the rheostat 6| which is connected in series relationship with the field wind- 7 ing 53a. of the generator 53 and the primary As the machine is brought to rest, the tension in the material naturally tends to disappear on account of the decrease in. current supplied to the winder motors 25 and 26. As the tension tends to decrease, the weights i1 and |1a rotate the contact arm 43. in a clockwise direction to a position on the resistor 43 such that the voltage applied to the field winding 40c causes the dy- .namoelectric machine 40 to excite the generator winding 6% is connected across the rheostat 52 which is connected in series relationship with the field winding 54.. of the calender stack motor 54.

When the resistance of the rheostat Si is decreased to increase the voltage supplied to the motors 5|, 52 and 54 to accelerate the machine, the voltage drop applied to the primary winding 55b is decreased and this decreasing voltage induces a. voltage in the secondary winding 60.; which is applied to the auxiliary control winding 55b of the dynamo, electric mach ne 551 The connections between the transformer and the field winding 55:, are such that the field windings 55 and 55s aci'zcumulatively thereby to armature reac-' before their speed could be changed as a result.

of the functioning of the tension responsive mechanism and consequently the winder motors 5| and 52 are maintained in step with the motor 54 during the acceleration so that tension changes in the web are substantially eliminated. If the acceleration is produced by varying the rheostat 62 to weaken the field of the calender stack motor 54, the changing voltage across the rheostat 62 is applied to the primary winding 60c of the transformer and a corresponding voltage induced in the secondary winding 60a. The connections of the primary winding 60c are such that the voltage induced in the secondary 60a produces a flux in the auxiliary field winding 55b which acts cumulatively with the flux of the main winding 55;; thereby to increase the current supplied to the winder motors 5| and 52.

When the rheostats 6i and 62 are varied in the reverse directions to produce deceleration of the machine, the voltages induced in the second ary winding 60a are of opposite polarity from 'those described in the foregoing and as a result the flux of the auxiliary field winding 55]: acts difierentially with respect to the flux of the field winding 559, so that the excitation of the field winding 59a is decreased and theamount of current supplied to the winder motors and 52 is correspondingly decreased. In Fig. 2, resistors 63 and 64 and rheostat 65 and 66 correspond to resistors 43 and 49 and rheostats 31 and 46, respectively, in Fig. 1 and perform identical functions. 1

Although in accordance with the provisions of the patent statutes this invention is described as embodied in concrete form and the principle of the invention has been explained together with the best mode in which it is now contemplated applying that principle, it will be understood that the apparatus shown and described is merely illustrative and that the invention is not limited thereto-since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claims. v

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. A control system for apparatus having an element operating on a length of material and a second element receiving said material from said first element comprising in combination electric motor means for driving said second element, driving means for said first element, a tachometer generator driven by said driving means, a

prising independent means controlled by the position of said movable element for controlling the supply of current tosaid motor means.

2. A control system for apparatus having a first element operating on a.length of material and a second element to which said material is second tachometer generator driven by said motor means. means responsive to the difference in the voltages of said tachometer generators for controlling the supply of current to said motor means to cause said second element to operate delivered from said first element comprising in combination electric motor means for driving said second element, means for controlling the supply of current to said motor means comprising a dynamo-electric machine provided with a control field winding, means for supplying a voltage to said control field winding proportional to the difference in speed of said elements thereby to cause said second element to operate at a speed proportional to the speed of said first element, and means for maintaining the tension of said material substantially constant during operation comprising an element movable in response to variations in said tension for varying the voltage supplied to said control field winding, and means for maintaining stalled tension in said material when said apparatus is stopped comprising means controlled by the position of said movable element for supplying an independent voltage to said control field winding.

3. A control system for apparatus having an element operating on a length of material and a second element to which said material is delivered from said first element comprising in com bination electric-motor means for driving said second element, means for controlling the supply of current to said motor means comprising a dynamo-electric machine provided with a control field winding, means for. causing said second element to operat at a speed proportional to the speed of said first element comprising a tachometer generator driven by said second element and a second tachometer generator driven by said first element and electrically connected difierentially with said first tachometer generator to said control field winding so that a voltage proportional to the difierence in speeds of said elements is supplied to said control field winding, and means for maintaining the tension in said material constant comprising an element movable in response to variation in said tension for varying the excitation of one of said tachometer generators.

4. A control system for apparatus having an element operating on a length of material and a second element receiving material from said first element comprising in combination, means for driving said first element, electric motor means for driving said second element, a tachometer.

generator driven by said driving means, a second tachometer generator driven by said motor means, means responsive to the difference in the voltages of said tachometer generators for controlling the supply of current to said motor means to cause said second element to operate at a speed proportional to the speed of said first element, and means for maintaining the tension of said material constant comprising an element movable in response to variation of said tension and a rheostat connected in the field circuit of one of said generators and actuated by said movable element.

5. A control system for apparatus having an element operating on a length of material and a second element receiving material from said first element comprising in combination, means for driving said first element, electric motor means for driving said second element, means for controlling the supply of current to said motor means comprising a dynamo-electric machine provided with a control field winding, means for causing said motormeans to operate at a speed proportionalto the speed of said driving means comprising a tachometer generator driven by said driving means, a second tachometer generator driven by said motor means and electrically connected difierentially with said first tachometer generator to said field winding so that a voltage proportional to the difierence in the speed of said driving means and motor means is supplied to said field winding, means for maintaining the tension of said material constant during operation comprising an element movable in response to variation of said tension for varying the excitation of one of said generators, and means for maintaining saidtension constant when said apparatus is stopped comprising means controlled by the position of said movable element for controlling the supply of an independent voltage to said field winding.

6. A control system for apparatus having an element operating on a length of material and a second element receiving material from said first element comprising in combination, means for driving said first element, electric motor means for driving said second element, means for controlling the supply of current to said motor means comprising a dynamo-electric machine provided with a control field winding means for causing said motor means to operate at a speed proportional to the speed of said driving means comprising a tachometer generator driven by said driving means, a, second tachometer generator, driven by said motor means and electrically connected diiferentially with said first tachometer generator to said field winding so that a voltage proportional to the difference in the speeds of said driving means and motor means is supplied to said field winding, means for maintaining the tension of said material constant during operation comprising an element movable in response to variation of said tension for varying the excitation of one of said generators, and means for maintaining said tension constant when said apparatus is stopped comprising connections from the field circuit of said motor means to said control field winding for supplying an independent voltage thereto and a rheostat included in said connections and actuated by said movable element for varying said independent voltage.

ing connected in the field-circuit of said generator, a second primary winding connected in the field circuit of said motor and a secondary winding connected to said field winding.

8. A control system for apparatus having an element operating on a length of material and a second element receiving the material from said first element comprising in combination an electric motor for driving said firstelement, electric motor means for driving said second element, a

generator for supplying said motor, means for controlling the supply of current to said motor eans comprising V a dynamo-electric machine having a control field winding, means for varying the speed of said motor comprising means for varying the excitation of said generator and means for varying the excitation of said motor, and means responsive to the rate of change of the field currents of said generator and said motor for controlling the excitation of said dynamoelectric machine to maintain tension in said material during acceleration and deceleration comprising a transformer having a primary winding connected in the field circuit of said generator, a second primary winding connected in the field circuit-of said motor and asecondary winding connected to said control field winding.

7. A control system for apparatus having an element operating on a length of material and a second element receiving the material delivered from said first element comprising in combination an electric motor for driving said first element, electric motor means for driving said second element, a generator for supplying the armature of said motor, means for varying the speed of said motor comprising means for varying the voltage supplied to said motor armature and means for varying the excitation of the field of said motor, means for controlling the supply of current to said motor means comprising a dynamo-electric machine having a field winding, means responsive to variations in the tension of said material for controlling the excitation of said dynamo-electric machine to counteract said tension variations, and means responsive to said armature'voltage varying means and said motor field excitation varying means for modifying the excitation of said dynamo-electric machine during acceleration and deceleration of said motor :omprising a transformer having a primary windcontrol field winding, means for 9. A control system for apparatus having an element operating on a length of material and a second element receiving the material from said first element comprising in combination an electric motor for driving said first element, electric motor means for driving said second element, a generator for supplying said motor and motor means, means for controlling the supply ofcurrent to said motor means comprising a dynamo-electric machine provided with a control field winding, means for varying the speed of said motor and said motor means comprising means for varying the excitation of said generator and means for varying the excitation of said motor, and means responsive to the rate of change of speed of said motor excitation of said dynamo-electric machine to increase the voltage supplied to said motor means during acceleration and to decrease the voltage supplied to said motor means during deceleration comprising a transformer having a primary winding connected in the field circuit of said tric motor means for driving said second ele-' ment, a generator for supplying said motor and motor means, means for controlling the supply of current to said motor means comprising a booster generator connected in circuit between said generator and motor means and a dynamoelectric machine connected to the field circuit of said booster generator and provided with a varying the speed of said apparatus comprising means for varying the excitations of said generator, motor and motor means, and means responsive to said excitation varying means for modifying the exdynamo-electric machine in accordance with the rate of change of speed of said apparatus to increase the voltage supplied to said motor means during acceleration and to for modifying the decrease the voltage supplied to said motor means during deceleration. comprising a transformer having a primary winding connected in the field circuit of said supply generator, a second primary winding connected in the field circuit of said motor and a secondary winding connected to the control field winding of said dynamo: electric machine.

11. A control system for apparatus having an element operating on a length of material and a second element receiving the material from said first element, an electric motor for driving said first element, electric motor means for driving said second element, a generator for supplying said motor, means for controlling the supply of current to said motor means comprising a first dynamo-electric machine having a field winding, means for maintaining the tension in the material between said elements constant comprising an armature reaction excited dynamo-electric machine provided with a control field winding and having its armature connected to the field winding of said first dynamo-electric machine and means responsive to variations in said tension for varying the excitation of said armature reaction excited dynamo-electric machine to counteract said variations in tension, means for varying the speed of said apparatus comprising means for varying the excitation of said generator, motor and motor means, and means responsive to said excitation varying means for modifying the excitation of said dynamo-electric machine in accordance with the rate of change of speed of said apparatus to increase the voltage supplied to said motor means during acceleration and to decrease the voltage supplied thereto during deceleration comprising a transformer having a primary winding connected in the field circuit of said generator, a second primary winding connected in the field circuit of said motor and a secondary winding connected to said control field winding.

12. A control system for apparatus having an element operating on a length of material and a second element receiving material delivered from said first element comprising in combination, an

electric motor for driving said first element, electric motor means for driving said second element, a generator for supplying said motor and motor means, means for controlling the supply of current to said motor means comprising a booster generator connected in circuit between said generator and motor means and a dynamoelectric machine provided with a. field winding and connected to control the excitation of said booster generator, and means for causing said motor means to operate in predetermined speed relationship with respect to said motor comprising a tachometer generator driven by said motor, a second tachometer generator driven by said motor means and electrically connected differentially with said first tachometer generator to said field winding.

13. A control system for apparatus having an element operating on a length of material and a second element receiving material delivered from said first element comprising in combination/an electric motor for driving said first element, electric motor means for driving said second element, a generator for supplying said motor and motor means, means for controlling the supply of current to said motor means comprising a booster generator connected in circuit between said generator and motor means and a dynamo-electric machine provided with a field winding and connected to control the excitation of said booster generator, means for causing said motor means to operate in predetermined speed relationship with respect to said motor comprising a tachometer generator driven by said motor, a second tachometer generator driven by said motor means and electrically connected differentially with said first tachometer generator to said field winding, and means for maintainingthe tension in said material between said element constant comprising an element movable in response to variations in said tension for varying the excitation of one of said tachometer generators to counteract said variations in tension MARTIN A. EDWARDS. DAVID R. SHOULTS. 

